Properties of substituted La-manganites are known to be very sensitive
to La site substitution, The critical parameters appear to be (a) the
charge and concentration of the substituted ions, which determine the
Mn3+/Mn4+ ratio, (b) the average ionic radius at the A site and (c) t
he tolerance factor, t, The latter two parameters determine the distor
tion and structural tuning of the perovskite structure, Here we report
the influence of minor variations in the above parameters on the magn
etotransport of compounds around the basic composition La0.6M0.07Ca0.3
3MnO3 (M = Er, Yb and Pi), The influence of the method of synthesis on
different properties is also discussed. The ionic radii of Er3+, Yb3 and Bi3+ ions are 1.00, 0.985 and 1.11 Angstrom, respectively, compar
ed to 1.32 Angstrom for La3+ and this provides a systematic variation
for the investigation of the effects of A site substitution. The zero
field resistivity data are essentially similar above the maxima which
corresponds, at least approximately, to the Curie temperature as deter
mined by magnetization measurements. However, there are variations bel
ow the transition temperature, where there is magnetic ordering, and l
arge variations are often seen in the magnetic data between samples wh
ich are very similar in composition, Substantial similarities between
field dependent magnetization and resistivity measurements appear to b
e related to domain wall displacement and rotation. These results will
be discussed in the framework of structural tuning which has a strong
influence on exchange parameters such as the Mn-O-Mn bond length and
angle.